What Is Sudden Cardiac Arrest?

Sudden cardiac arrest (SCA) is a condition in which the heart suddenly and unexpectedly stops beating. When this happens, blood stops flowing to the brain and other vital organs.

SCA usually causes death if it's not treated within minutes.

Overview

To understand SCA, it helps to understand how the heart works. The heart has an internal electrical system that controls the rate and rhythm of the heartbeat. Problems with the electrical system can cause abnormal heart rhythms called arrhythmias (ah-RITH-me-ahs).

There are many types of arrhythmias. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Some arrhythmias can cause the heart to stop pumping blood to the body. These are the type of arrhythmias that cause SCA.

SCA is not the same as a heart attack. A heart attack occurs when blood flow to part of the heart muscle is blocked. During a heart attack, the heart usually doesn't suddenly stop beating. SCA, however, may happen after or during recovery from a heart attack.

People who have heart disease are at increased risk for SCA. However, most SCAs happen in people who appear healthy and have no known heart disease or other risk factors for SCA.

Outlook

Ninety-five percent of people who have SCA die from it—most within minutes. Rapid treatment of SCA with a defibrillator can be lifesaving. A defibrillator is a device that sends an electric shock to the heart to try to restore its normal rhythm.

Automated external defibrillators (AEDs), which often are found in public places like airports and office buildings, can be used by bystanders to save the lives of people who are having SCA.

What Causes Sudden Cardiac Arrest?

Most cases of sudden cardiac arrest (SCA) are due to ventricular fibrillation (v-fib). V-fib is a type of arrhythmia. In v-fib, the ventricles (the heart's lower chambers) don't beat normally. Instead, they quiver very rapidly and irregularly.

When this happens, the heart pumps little or no blood to the body. V-fib is fatal if not treated within a few minutes.

Other electrical problems in the heart also can cause SCA. For example, SCA can occur if the rate of the heart's electrical signals becomes very slow and stops. SCA also can occur if the heart muscle doesn't respond to the heart's electrical signals.

Several factors can cause the electrical problems that lead to SCA. These factors include:

• Coronary artery disease (CAD), which reduces blood flow to the heart muscle
• Severe physical stress, which raises the risk for abnormal electrical activity in the heart
• Inherited disorders that disrupt the heart's electrical activity
• Structural changes in the heart that cause electrical signals to spread abnormally

Several research studies are under way to try to find the exact causes of SCA and how to prevent them.

Coronary Artery Disease

CAD occurs when a fatty material called plaque (plak) builds up in the coronary arteries. These arteries supply your heart muscle with oxygen-rich blood.

Plaque narrows the arteries and reduces blood flow to your heart muscle. Eventually, an area of plaque can rupture, causing a blood clot to form on the surface of the plaque.

A blood clot can mostly or completely block the flow of oxygen-rich blood to the part of the heart muscle fed by the artery. This causes a heart attack.

During a heart attack, some heart cells die and are replaced by scar tissue. This damages the heart's electrical system. The scar tissue may cause electrical signals to spread abnormally throughout the heart. These changes increase the risk for dangerous ventricular arrhythmias and SCA.

CAD seems to be the cause of most cases of SCA in adults. Many of these adults, however, have no signs or symptoms of CAD before having SCA.

Physical Stress

Certain types of physical stress can cause your heart's electrical system to fail. Examples include:

• Intense physical activity. The hormone adrenaline is released during intense physical activity. This hormone can trigger SCA in people who have other heart problems.
• Very low blood levels of potassium or magnesium. These minerals play an important role in your heart's electrical signaling.
• Major blood loss.
• Severe lack of oxygen.

Inherited Disorders

A tendency to have arrhythmias runs in some families. This tendency is inherited, which means it's passed from parents to children. Members of these families may be at increased risk for SCA.

An example of an inherited disorder that makes you more likely to have arrhythmias is long QT syndrome (LQTS). LQTS is a disorder of the heart's electrical activity due to problems with tiny pores on the surface of heart muscle cells. LQTS can cause sudden, uncontrollable, dangerous heart rhythms.

People who inherit structural heart problems also may be at increased risk for SCA. Many cases of SCA in children are due to these problems.

Structural Changes in the Heart

Changes in the heart's normal size or structure may affect its electrical system. Examples of such changes include an enlarged heart due to high blood pressure or advanced heart disease. Heart infections also may cause structural changes in the heart.

Who Is At Risk for Sudden Cardiac Arrest?

Each year, between 250,000 and 450,000 Americans have sudden cardiac arrest (SCA). SCA occurs most often in people in their mid-thirties to mid-forties. It appears to affect men twice as often as women.

SCA rarely occurs in children unless they have inherited problems that make them likely to have SCA. Only a very small number of children have SCA each year.

Major Risk Factors

The major risk factor for SCA is undiagnosed coronary artery disease (CAD). Most people who have SCA are later found to have some degree of CAD. Most of these people don't know that they have CAD until SCA occurs.

Their CAD is "silent"—that is, it has no signs or symptoms. Because of this, doctors and nurses have not detected it. Most cases of SCA happen in people who have silent CAD and who have no known heart disease prior to SCA.

Many people who have SCA also have a silent, or undiagnosed, heart attack before SCA happens. These people have no obvious signs of heart attack, and they don't even realize that they've had one. The chances for having SCA are higher during the first 6 months after a heart attack.

For more information about CAD risk factors, see "Who Is At Risk for Coronary Artery Disease?"

Other Risk Factors

Other risk factors for SCA include:

• A personal or family history of SCA or of inherited disorders that make you prone to arrhythmias
• A history of having arrhythmias
• Heart attack
• Heart failure
• Drug abuse or excessive alcohol intake

What Are the Signs and Symptoms of Sudden Cardiac Arrest?

Usually, the first sign of sudden cardiac arrest (SCA) is loss of consciousness (fainting). At the same time, no heartbeat (or pulse) can be felt.

Some people may have a racing heartbeat or feel dizzy or lightheaded just before they faint. Within an hour before SCA, some people have chest pain, shortness of breath, nausea (feeling sick to the stomach), or vomiting.

How Is Sudden Cardiac Arrest Diagnosed?

Sudden cardiac arrest (SCA) happens without warning. It requires immediate emergency treatment. Doctors rarely can diagnose SCA with medical tests as it's happening.

Instead, SCA often is diagnosed after it happens. Doctors do this by ruling out other causes of a person’s sudden collapse.

Specialists Involved

If you're at high risk for SCA, you may see a cardiologist. This is a doctor who specializes in heart diseases and conditions. Your cardiologist will work with you to decide whether you need treatment to prevent SCA.

Some cardiologists specialize in problems with the heart’s electrical system. These specialists are called cardiac electrophysiologists.

Diagnostic Tests and Procedures

Doctors use several tests to help detect the factors that put people at risk for SCA.

EKG (Electrocardiogram)

An EKG is a simple, painless test that records the heart's electrical activity. This test is used to detect and locate the source of several heart problems.

An EKG shows how fast the heart is beating and the heart's rhythm (steady or irregular). It also records the strength and timing of electrical signals as they pass through each part of the heart.

An EKG may show whether you’ve had a heart attack.

Echocardiography

Echocardiography (EK-o-kar-de-OG-ra-fee) is a painless test that uses sound waves to create pictures of your heart. It provides your doctor with information about the size and shape of your heart and how well your heart's chambers and valves are working.

The test also can find areas of heart muscle that aren’t contracting normally due to poor blood flow or injury from a previous heart attack.

There are several different types of echocardiography, including stress echocardiography. This type is done both before and after a cardiac stress test. During this test, you exercise or take medicine (given by your doctor) to make your heart work hard and beat fast.

Stress echocardiography shows whether you have decreased blood flow to your heart (a sign of coronary artery disease).

MUGA Test or Cardiac Magnetic Resonance Imaging

A MUGA test shows how well your heart is pumping blood. For this test, a small amount of radioactive substance is injected into a vein and travels to your heart. The substance releases energy, which special cameras outside of your body detect. The cameras use the energy to create pictures of different parts of your heart.

Cardiac magnetic resonance imaging (MRI) is a safe procedure that uses radio waves and magnets to create detailed pictures of your heart. The test creates images of your heart as it is beating, producing both still and moving pictures of your heart and major blood vessels.

Doctors use cardiac MRI to get images of the beating heart and to look at the structure and function of the heart.

Cardiac Catheterization

Cardiac catheterization is a procedure used to diagnose and treat certain heart conditions. A long, thin, flexible tube called a catheter is put into a blood vessel in your arm, groin (upper thigh), or neck and threaded to your heart. Through the catheter, your doctor can do diagnostic tests and treatments on your heart.

Sometimes a special dye is put into the catheter to make the inside of your heart and blood vessels show up on x rays. The dye can show whether plaque has narrowed or blocked any of your coronary arteries.

Electrophysiology Study

For an electrophysiology study, doctors use cardiac catheterization to record how your heart's electrical system responds to certain medicines and electrical stimulation. This helps your doctor find where the heart's electrical system is damaged.

Blood Tests

You may have blood tests to check the levels of potassium, magnesium, and other chemicals in your blood that play an important role in your heart's electrical signaling.

How Is Sudden Cardiac Arrest Treated?

Emergency Treatment

Sudden cardiac arrest (SCA) requires immediate treatment with a defibrillator. This device sends an electric shock to the heart. The electric shock may restore a normal rhythm to a heart that's stopped beating.

To work well, defibrillation must be done within minutes of SCA. With every minute that passes, the chances of surviving SCA drop rapidly.

Police, emergency medical technicians, and other first responders usually are trained and equipped to use a defibrillator. Call 9–1–1 right away if someone has signs or symptoms of SCA. The sooner help is called, the sooner potentially lifesaving treatment can be done.

Automated External Defibrillators

Automated external defibrillators (AEDs) are special defibrillators that untrained bystanders can use. These devices are becoming more available in public places like airports, office buildings, and shopping centers.

AEDs are programmed to give an electric shock if they detect a dangerous arrhythmia, such as ventricular fibrillation. This prevents giving a shock to someone who may have fainted but isn't having SCA.

Cardiopulmonary resuscitation (CPR) should be given to a person having SCA until defibrillation can be done.

People who are at risk for SCA may want to consider having an AED at home. Currently, one AED, the Phillips HeartStart Home Defibrillator, is sold over-the-counter for home use.

The benefits of home-use AEDs are still debated. Some people feel that placing these devices in homes will save many lives, because many SCAs occur at home.

Others note that no evidence supports the idea that home-use AEDs save more lives. These people fear that people who have AEDs in their homes will delay calling for help during an emergency. They’re also concerned that people who have home-use AEDs will not properly maintain the devices or forget where they are.

A large study on AEDs is currently under way. It may provide information on the pros and cons of having an AED in the home.

When considering a home-use AED, talk to your doctor. He or she can help you decide whether having an AED in your home will benefit you.

Treatment in a Hospital

If you survive SCA, you usually will be admitted to a hospital for observation and treatment. In the hospital, your medical team will closely watch your heart. They may give you medicines to try to reduce the chance of another SCA.

While in the hospital, your medical team will try to find out what caused your SCA. If you're diagnosed with coronary artery disease, you may have angioplasty or coronary artery bypass grafting. These procedures help restore blood flow through narrowed or blocked coronary arteries.

Often, people who have SCA get a device called an implantable cardioverter defibrillator (ICD). This small device is surgically placed under the skin in your chest or abdomen. An ICD uses electric pulses or shocks to help control dangerous arrhythmias. (For more information, see "How Can Death Due to Sudden Cardiac Arrest Be Prevented?")

How Can Death Due to Sudden Cardiac Arrest Be Prevented?

Ways to prevent death due to sudden cardiac arrest (SCA) differ depending on whether:

• You've already had SCA
• You've never had SCA but are at high risk for the condition
• You've never had SCA and have no known risk factors for the condition

For People Who Have Survived Sudden Cardiac Arrest

If you've already had SCA, you're at high risk of having it again. Research shows that an implantable cardioverter defibrillator (ICD) reduces the chances of dying from a second SCA.

An ICD is surgically placed under the skin in your chest or abdomen. The device has wires with electrodes on the ends that connect to your heart's chambers. The ICD monitors your heartbeat.

If the ICD detects a dangerous heart rhythm, it gives an electric shock to restore the heart's normal rhythm. Your doctor may give you medicine to limit irregular heartbeats that can trigger the ICD.

Implantable Cardioverter Defibrillator

The illustration shows the location of an implantable cardioverter defibrillator in the upper chest. The electrodes are inserted into the heart through a vein.

An ICD isn't the same as a pacemaker. The devices are similar, but have some differences. Pacemakers only give off low-energy electrical pulses. They're often used to treat less dangerous heart rhythms, such as those that occur in the upper chambers of the heart. Most new ICDs work as both pacemakers and ICDs.

For People at High Risk for a First Sudden Cardiac Arrest

If you have severe coronary artery disease (CAD), you're at increased risk for SCA. This is especially true if you've recently had a heart attack.

Your doctor may prescribe a type of medicine called a beta blocker to help lower your risk for SCA. Other treatments for CAD, such as angioplasty or coronary artery bypass grafting, also may lower your risk for SCA.

Your doctor also may recommend an ICD if your risk for SCA is very high.

For People Who Have No Known Risk Factors for Sudden Cardiac Arrest

CAD seems to be the cause of most cases of SCA in adults. CAD also is a major risk factor for angina (chest pain or discomfort) and heart attack, and it contributes to other heart problems.

Following a healthy lifestyle can help you lower your risk for CAD, SCA, and other heart problems.

Healthy Diet and Physical Activity

A healthy diet is an important part of a heart healthy lifestyle. Choose a variety of fruits, vegetables, and grains; half of your grains should come from whole-grain products.

Choose foods that are low in saturated fat, trans fat, and cholesterol. Healthy choices include lean meats, poultry without skin, fish, beans, and fat-free or low-fat milk and milk products.

Choose and prepare foods with little sodium (salt). Too much salt can raise your risk for high blood pressure. Recent studies show that following the Dietary Approaches to Stop Hypertension (DASH) eating plan can lower blood pressure.

Choose foods and beverages that are low in added sugar. If you drink alcoholic beverages, do so in moderation.

Aim for a healthy weight by staying within your daily calorie needs. Balance the calories you take in with the calories you use while doing physical activity. Be as physically active as you can.

Some people should get medical advice before starting or increasing physical activity. For example, talk to your doctor if you have a chronic (ongoing) health problem, are on medicine, or have symptoms such as chest pain, shortness of breath, or dizziness. Your doctor can suggest types and amounts of physical activity that are safe for you.

For more information on following a healthy diet, see the National Heart, Lung, and Blood Institute's (NHLBI's) Aim for a Healthy Weight Web site, "Your Guide to a Healthy Heart," and "Your Guide to Lowering Your Blood Pressure With DASH." All of these resources provide general information about healthy eating.

For more information about physical activity, see NHLBI's "Your Guide to Physical Activity and Your Heart."

Other Lifestyle Changes

Other lifestyle changes also can help lower your risk for SCA. Examples include:

• Quitting smoking. Talk to your doctor about programs and products that can help you quit. Also, try to avoid secondhand smoke.
• Losing weight if you're overweight or obese.
• Treating other health problems, such as high blood pressure, high blood cholesterol, and diabetes.

Key Points

• Sudden cardiac arrest (SCA) is a condition in which the heart suddenly and unexpectedly stops beating. When this happens, blood stops flowing to the brain and other vital organs.
• SCA usually causes death if it's not treated within minutes.
• SCA usually occurs when the heart develops an arrhythmia (irregular heartbeat) that causes the heart to stop pumping blood to the body.
• SCA is not the same as a heart attack. During a heart attack, the heart usually doesn’t stop beating. SCA, however, can happen after or during recovery from a heart attack.
• Most cases of SCA are due to an arrhythmia called ventricular fibrillation. Other electrical problems in the heart also can cause SCA. Several factors can cause the electrical problems that lead to SCA. These factors include coronary artery disease (CAD), severe physical stress, inherited disorders, and structural changes in the heart.
• SCA occurs most often in people in their mid-thirties to mid-forties. It affects men twice as often as women. The major risk factor for SCA is undiagnosed CAD.
• Usually, the first sign of SCA is loss of consciousness (fainting). At the same time, no heartbeat (or pulse) can be felt. Some people may have a racing heartbeat, dizziness, lightheadedness, chest pain, shortness of breath, nausea (feeling sick to the stomach), or vomiting before SCA.
• SCA often happens without warning. It requires immediate emergency treatment. Doctors rarely have a chance to diagnose SCA with medical tests as its happening. Instead, SCA usually is diagnosed after it happens. Doctors do this by ruling out other causes of a person's sudden collapse.
• SCA requires immediate treatment with a defibrillator. This device sends an electric shock to the heart. The shock may restore a normal rhythm to a heart that's stopped beating. To work well, defibrillation much be done within minutes of SCA.
• Automated external defibrillators (AEDs) are special defibrillators that untrained bystanders can use. These devices are becoming more available in public places like airports, office buildings, and shopping centers.
• If you survive SCA, you usually will be admitted to a hospital for observation and treatment. Your medical team will try to find out what caused your SCA. If you're diagnosed with CAD, you may have angioplasty or coronary artery bypass grafting. These procedures help restore blood flow through narrowed or blocked coronary arteries.
• Often, people who have SCA get a device called an implantable cardioverter defibrillator (ICD) to prevent a repeat SCA. This small device is surgically placed under the skin in your chest or abdomen. An ICD uses electric pulses or shocks to help control dangerous arrhythmias.
• Talk to your doctor about ways to prevent death due to SCA. Medical devices, medicines, and lifestyle changes can lower your risk for SCA. What steps you should take depend on if you've already had SCA, if you've never had SCA but are at high risk for the condition, or if you've never had SCA and have no known risk factors for the condition.

Links to Other Information About Sudden Cardiac Arrest

NHLBI Resources

• Arrhythmia (Diseases and Conditions Index)
• Coronary Artery Disease (Diseases and Conditions Index)
• Implantable Cardioverter Defibrillator (Diseases and Conditions Index)
• "Your Guide to Living Well With Heart Disease"

Non-NHLBI Resources

• Cardiac Arrest (MedlinePlus)

Clinical Trials

• Current Research (ClinicalTrials.gov)